1. Field of the Invention
The invention relates to a miniaturized antenna with at least a ceramic substrate and a metallization, in particular for use in the high-frequency and microwave range. The invention further relates to a printed circuit board and a mobile telecommunication device with such an antenna.
2. Description of the Related Art
Following the trend towards ever smaller electronic components, in particular in the field of telecommunication technology, all manufacturers of passive and/or active electronic components are intensifying their activities in this field. Particular problems then arise especially with the use of electronic components in the high-frequency and microwave technology fields, because many properties of the components are dependent on their physical dimensions. This is based on the generally known fact that the wavelength of the signal becomes smaller with increasing frequency, which again has the result that the supplying signal source is influenced in particular by reflections.
It is in particular the structure of the antenna of such an electronic device, for example a mobile telephone, which is more strongly dependent on the desired frequency range of the application than that of any other HF component. This is caused by the fact that the antenna is a resonant component which is to be adapted to the respective application, i.e. the operating frequency range. In general, wire antennas are used for transmitting the desired data. Certain physical lengths are absolutely necessary for obtaining good radiation and reception properties for these antennas.
So-called xcex/2 dipole antennas, whose length corresponds to half the wavelength (xcex) of the signal in open space, have optimum radiation properties. The antenna is composed of two wires each xcex/4 long which are rotated through 180xc2x0 with respect to one another. Since these dipole antennas are too large for many applications, however, in particular for mobile telecommunication (the wavelength for the GSM900 range is, for example, approximately 32 cm), alternative antenna structures are utilized. A widely used antenna in particular for the mobile telecommunication bands is the so-called xcex/4 monopole. This is formed by a wire with a length of xcex/4. The radiation behavior of this antenna is acceptable while at the same time its physical length (approximately 8 cm for GSM900) is satisfactory. This type of antenna in addition is characterized by a great impedance and radiation bandwidth, so that it can also be used in systems which require a comparatively great bandwidth. To achieve an optimum power adaptation to 50 xcexa9, a passive electrical adaptation is chosen for this type of antenna, as is also the case for most xcex/2 dipoles. This adaptation is usually formed by a combination of at least one coil and a capacitance, which adapts the input impedance of the xcex/4 monopole different from 50 xcexa9 to the connected 50 xcexa9 components by a suitable dimensioning.
Although antennas of this type are widely used, they do have considerable disadvantages. One of these is the passive adaptation circuit mentioned above.
Furthermore, the xcex/4 monopoles cannot be directly soldered onto the printed circuit board because the wire antennas are mostly used as pull-out members, for example in mobile telephones. This means that expensive contacts are necessary for the information exchanged between the printed circuit board and the antenna.
A further disadvantage of antennas of this type is the mechanical instability of the antenna itself as well as the adaptation of the housing to the antenna made necessary by this instability. If a mobile telephone, for example, is dropped, the antenna will usually break off, or the housing is damaged in that location where the antenna can be pulled out.
Chip antennas with a substrate and at least one conductor are indeed known from EP 0 762 538. These antennas, however, have the disadvantage that at least portions of the conductor tracks extend inside the substrate, and that accordingly the substrate is to be manufactured in several layers and with a certain minimum size, which may be comparatively expensive. In addition, it is not possible with this arrangement of the conductor tracks to carry out an electrical adaptation of the conductor tracks to a concrete constructional situation in the finished state, because the conductor track is no longer accessible, or only partly accessible.
The invention accordingly has for its object to provide an antenna with at least a ceramic substrate and a metallization, in particular for use in high-frequency and microwave ranges, which has a high mechanical stability and is particularly suited for miniaturization.
Furthermore, an antenna is to be provided which renders it possible to dispense at least substantially with passive adaptation circuits and which is also suitable for surface mounting by the SMD (surface mounting device) technology on a printed circuit board.
Finally, an antenna is to be provided with a sufficiently great resonance frequency and impedance bandwidth for operation in the GSM or UMTS bands.
This object is achieved by an antenna having a surface metallization which is formed by a feed terminal for electromagnetic energy to be radiated, at least a first metallization structure, and a conductor track extending along at least a portion of the circumference of the substrate, which track connects the feed terminal to the at least one first metallization structure, while said first metallization structure comprises a first conductor track portion extending from a side of the substrate opposite the feed terminal towards the feed terminal and comprises a first metallization pad.
This solution combines many advantages. Since the feed terminal is part of the metallization present on the surface of the substrate, no contact pins or similar items are required for feeding-in of the electromagnetic energy to be radiated. This means that the antenna can be provided by surface mounting (SMD technology) on a printed circuit board (together with the other components). The size of the antenna can also be further reduced thereby, and the antenna is mechanically substantially more stable and insensitive to external influences.
It was also found that passive circuits for impedance adaptation are unnecessary, because such an adaptation can be achieved through a change in the fully accessible metallization (for example achieved by laser trimming) with the antenna in the incorporated state. It was also found that the antenna has a surprisingly great impedance and radiation bandwidth.